I agree with ElliotS that Ethiopia's AI flavor personality syncs really well with their Uniques and VP as a whole. They try to found a religion early and spread it as far as possible, but are also very friendly unless attacked, as they care very much about defending themselves. I see Ethiopia do very well unless they start next to 1-2 warmonger AIs that can sack them before they have a chance to really get going. If Ethiopia can found a religion and start spreading it before they face a serious military threat they tend to do very well for the whole game. There are a few hard counters to them (I see Attila and Zulu smush them in the Ancient/Early Classical Era all the time, or try and take their holy city if it ends up not being their capital; England is good at leeching off their early tech lead), but as a human player I don't find them to be a huge threat unless I am playing as a Civ that also wants a strong religion with lots of followers.